1. Field of the Invention
The present invention relates to a battery module comprising multiple battery cells.
2. Description of the Related Art
In recent years, a secondary battery is employed in electronic devices and industrial equipment, employed as a household rechargeable battery, and employed as a power source for hybrid vehicles, plug-in hybrid vehicles, electric vehicles, etc. Currently, a lithium ion battery has become broadly popular as such a secondary battery. Furthermore, development of such a lithium ion battery having a large battery capacity has been being advanced. However, such a lithium ion battery has a large internal impedance, leading to a problem in that it is difficult to draw a large current from such a lithium ion battery.
In view of such a situation, there are indications that an electric double-layer capacitor will become popular, as a replacement for such a lithium ion battery. An electric double-layer capacitor has a low input impedance, as compared with a lithium ion battery. Thus, such an electric double-layer capacitor has an advantage of allowing the user to easily draw an instantaneous large current. For example, a related technique has been disclosed in Japanese Patent Application Laid Open No. 2002-246071.
FIG. 1 is a circuit diagram showing a configuration of a power supply circuit 2r according to a first comparison technique investigated by the present inventors. With the first comparison technique, a battery module 10r includes multiple, i.e., N (N represents an integer of 2 or more) battery cells (capacitor cells) CC1 through CCN stacked in series, a charger circuit 110, and a cell balance circuit 120. It should be noted that the power supply circuit 2r investigated by the present inventors shown in FIG. 1 is by no means regarded as a known technique.
The sum total of the terminal voltages (cell voltages) Vc1 through VcN of the multiple battery cells CC1 through CCN is supplied as an output voltage (which will also be referred as the “battery voltage”) VBAT that develops between an anode terminal 12 and a cathode terminal 14.
Upon receiving the supply of the input voltage VIN from an external circuit, the charger circuit 110 is configured to charge the capacitor cells CC1 through CCN. Because there are irregularities in the electrical characteristics of the capacitor cells CC1 through CCN, if such capacitor cells CC1 through CCN are charged without any countermeasure for compensating for such irregularities, it leads to a problem in that there is a difference between the cell voltages Vc1 through VcN. In order to solve such a problem, when the input voltage vIN is supplied, the cell balance circuit 120 is configured to operate so as to stabilize the voltages at the tap electrodes TC1 through TCN-1 to a predetermined level such that the multiple cell voltages Vc1 through VcN become the same voltage level.
It should be noted that the cell balance circuit 120 is arranged such that the input voltage VIN is supplied to a power supply terminal 122 of the cell balance circuit 120. Thus, in a state in which the input voltage VIN is not supplied, i.e., when the battery cells are not charged, the cell balance circuit 120 enters the non-operating state. Thus, wasted electric power consumption does not occur.
Typically, in a case of supplying a voltage to a load 4a configured to operate at a voltage level on the order of the battery voltage VBAT, the battery voltage VBAT is supplied as-is to the load 4a. However, in a case of supplying a voltage to a load 4b configured to operate at a voltage level that is significantly lower than the battery voltage VBAT, there is a need to step down the battery voltage VBAT by means of a switching regulator (DC/DC converter) 6 before the operating voltage is supplied to the load 4b. 